1. Field of the Invention
This invention relates to a technique applied to a constraint satisfaction problem, in which a value is allocated to a variable in order to satisfy a constraint condition.
2. Description of the Related Art
Conventionally, in investigating an appropriate transshipment method for steel products or the like at a steel plant, such a model as described below is conceived.
Three loading locations, namely, a location A, location B, and location C are envisaged as loading locations for a steel product or the like. The location A is a place where physical objects for transshipment (hereinafter simply referred to as “object”) are initially loaded, while the location C is a final place for loading the objects. The location B is along a transfer path of the objects between the location A and location C, and is a place to transship the objects temporarily from the location A thereto, and transship the objects therefrom to the location C into a desired loading state.
As a specific example of such a model, from a warehouse 1 which is the location A, objects are transshipped and loaded on a truck (corresponding to the location B), and the loaded objects are transferred to the location C by the truck. Subsequently, in the location C, the objects are transshipped into a desired loading state.
Here, when heavyweight objects such as steel product is handled in particular, the following constraint conditions are placed in conceiving a transshipment method of the objects. One condition is that in the both cases where the objects are transshipped from the location A to the location B, and the objects are transshipped from the location B to the location C, the objects have to be taken out in an order beginning from an object loaded at an upper level in the original location, and another condition is that an object transferred earlier among the objects to be loaded in the same transshipping location has to be loaded at a lower level of the transshipping location.
Conventionally, a constraint satisfaction solution allowing a desired loading state in the location C is obtained by covering, as the solution search target, a solution space consisting of a set of solution candidates simulating transferring procedures of each object, and by detecting a solution candidate which satisfies the above constraint conditions.    [Patent Document 1] Japanese Patent No. 2951167    [Patent Document 2] Japanese Patent No. 3243058    [Patent Document 3] Japanese Patent Application Laid-open No. Hei 5-173999    [Patent Document 4] Japanese Patent Application Laid-open No. Hei 5-233597    [Patent Document 5] Japanese Patent Application Laid-open No. Hei 5-28126
However, conventionally, the enormity of the scale of the solution space targeted for solution search is seen as a problem. That is to say, the enormity of the scale of the solution space causes an extravagant processing time for the solution search processing in which a constraint satisfaction solution is searched out of the solution space, which is regarded as a serious problem.